When a rotor blade with a leading edge and a trailing edge is exposed to a fluid, such as air, flowing substantially from the leading edge to the trailing edge of the rotor blade, noise is generally generated at the edges of the rotor blade. The intensity of the noise and the frequency of the noise depend on many parameters, such as the properties of the fluid and the properties of the edge, namely the size of the edge and the shape of the edge, e.g. whether it is rounded or sharp.
The noise being generated at the edges is typically undesired. In the example of a wind turbine which is installed onshore, i.e. at the ground, noise which is generated by the rotating rotor blades can be perceived as a nuisance by people in the vicinity of the wind turbine. For this reason, there exist various legal provisions and restrictions regarding the noise level which is allowed to be produced by such a wind turbine at a certain distance from the wind turbine. As a consequence, wind turbines may either need to be placed further away from residential areas or they have to be operated in such a manner that the maximum allowed level of noise is not exceeded. This means that wind turbines may need to be curtailed in certain conditions because of the flow-induced edge noise.
As this issue is known since several years, various approaches for reducing flow-induced edge noise of a rotor blade have been proposed. These approaches include the shape and the design of the airfoil. In this context, particularly the shape and the design of the trailing edge of the rotor blade is of utmost importance. Aerodynamic add-ons may be added to or included in the rotor blade in order to minimize the flow-induced edge noise of the rotor blade. Well-known add-ons for noise reduction are serrations such as a serrated panel which is mounted to the pressure side or suction side of the rotor blade close to the trailing edge. However, the still existing and the still generated flow-induced edge noise could still be considerable.
Thus, there exists the desire to provide a concept how to further reduce flow-induced edge noise of a rotor blade.